At present, the concept of a Timing Advance (TA) Group (TA group) has been accepted to support multiple TA values in the R11. With a TA group, cells (including a primary cell (Pcell) and secondary cells (Scells)) sharing the same TA value are grouped into the same TA group, and Scells which do not share the same TA value as the Pcell are grouped into a TA group different from the Pcell. Furthermore Scells with the same TA value will be grouped into the same TA group. With the introduction of a TA group, each TA group has to be identified with a TA Group Identifier (TAG ID). Thus it is desirable to address where the TA identifier is identified and when and where a value of a Time Alignment Timer (TAT) for the TA group will be transmitted.
In some proposals, it is proposed to transmit a TAG ID when a Scell is being configured (for example, when the Scell is being added to a UE) or during MAC activation. In the majority of configuration scenarios, either of the foregoing two schemes can work well because a base station can obtain a network deployment characteristic via an Operation and Maintenance (OAM) command. With the presence of a repeater (particularly an ad-hoc repeater), the foregoing schemes may require subsequent Radio Resource Control (RRC) connection reconfiguration or MAC activation to reassign a TA group because a base station may have not assigned a correct TA group during initial reconfiguration or MAC activation in that at that time the base station did not know the location of the UE, that is, the base station did not know whether the UE is in the repeater.
For example, the following two scenarios will be studied:
In a first scenario, the base station assumes that a UE is in a coverage range of the repeater and assigns a new TA group for the Scell.
In a second scenario, the base station assumes that the UE is not in the coverage range of the repeater, and the base station assigns an existing TA group for the Scell.
For the first scenario, the base station may have to reassign an existing TA group for the Scell of the UE if the UE is not in the coverage range of the repeater, thus requiring subsequent RRC or MAC signaling.
For the second scenario, if the UE is in the coverage range of the repeater, then the base station detects that the UE is in the coverage range of the repeater and then will not know a specific existing TA group to be reassigned until it receives a pilot from the user equipment.
No proposal has been made so far as to the problem of when/where to transmit or release a TAT value of a TA group including only Scells. However when a TA group includes a Pcell, a TAT value will be transmitted when the Pcell is established (that is, during establishment or reestablishment of an RRC connection) or the Pcell is changed as stated in the Release 10 (Rel-10).